Insights into the Correlation of Aluminum Distribution and Brönsted Acidity in H-Beta Zeolites from Solid-State NMR Spectroscopy and DFT Calculations

Abstract

Here we utilized Al MAS/MQMAS andP MAS NMR of quantitative adsorption of trimethylphosphine oxide (TMPO) and DFT calculations to elucidate the relationship between Al distribution and Brönsted acidity of series H-Beta zeolites derived from dealumination of Al-rich H-Beta zeolite. Three types of Brönsted acid strengths corresponding to different specific Al T-sites were demonstrated. The removal of one framework Al in 5MR2--2Al and 6MR-2Al sites led to increasing the Brönsted acid strength of dealuminated H-Beta. Our findings on such exact correlation between specific Al distributions and corresponding Brönsted acid sites may guide the controlling Al distribution to get desired acid properties through zeolite synthesis or finely tuned dealumination, which has a great impact on the catalytic activity and selectivity of zeolite catalysts.

Insight into the active site nature of zeolite H-BEA for liquid phase etherification of isobutylene with ethanol

“…90 The higher ammonia adsorption heat for silanol groups of zeolites, compared with silanols in silica, may be associated with the induced action of aluminum. 21,91 An increase of the aluminum content for H-BEA zeolite is accompanied by an increase in E NH 3 for weak acid sites as it follows from the data presented in Table 2.…”

A Practical Review of NMR Lineshapes for Spin-1/2 and Quadrupolar Nuclei in Disordered Materials

“…DFT (Density Functional Theory) calculations have been used to directly relate NMR parameters to structural differences and variations, modeled either as many distinct crystalline sites or continuous distributions from disorder. [11] Such an approach has prompted increased interest in recent research in heterogeneous catalysis, such as revealing aluminum/proton site distributions in zeolite [32,35,36] and amorphous silica-alumina catalysts [37].…”

Excellent Performances of Dealuminated H‐Beta Zeolites from Organotemplate‐Free Synthesis in Conversion of Biomass‐derived 2,5‐Dimethylfuran to Renewable p‐Xylene

“…Besides the peak of physisorbed TMPO around 43 ppm, the peaks with 31 PNMR chemicals hifts from 50 to 84 ppm are ascribed to chemically adsorbed TMPO on Brønsted or Lewis acid sites. [40][41][42] Accordingt oo ur previous study, [42] the peaks at about 83, 69, and 55-62 ppm are assigned to TMPO adsorbed on the strong, medium-strength, and weakB rønsted acid sites, respectively,a nd those at 65 and 50 ppm to TMPO adsorbed on the Lewis acid sites. Figure 6s hows that H-beta-22f rom dealumination of Al-rich H-beta-7 has more medium-strength Brønsteda cid sites than the commercial H-beta-19.…”

“…The dealuminated H‐beta zeolites with Si/Al=22 and 36 were obtained by treating the parent Al‐rich H‐beta with 4–15 % aqueous HNO 3 solution at 50–100 °C, collected by filtration, washed with deionized water, and dried at 110 °C. Commercial beta zeolite with Si/Al=19 from organotemplate synthesis (CP814C, NH 4 + form, Zeolyst) was converted to the H + form by calcination at 550 °C for 4 h. As demonstrated in our previous report, all samples show good BEA structure in XRD patterns, and their Si/Al ratios in the framework were determined by deconvolution of the corresponding 29 Si MAS NMR spectra. To remove the extra‐framework Al in H‐beta (Si/Al=22), 1.0 mol L −1 hydrochloric acid was added to an aqueous suspension of the zeolite, and then the pH value was adjusted to 1.0 over 3 h. The suspension was stirred for 16 h at room temperature, filtered, and the solid dried at 110 °C.…”

“…All organotemplate-free beta zeolites were provided by BASF SE, Germany,a nd their synthesis procedures were reported elsewhere. [22,23] [42] all samples show good BEA structure in XRD patterns, and their Si/Al ratios in the framework were determined by deconvolution of the corresponding 29 Si MAS NMR spectra. To remove the extra-framework Al in H-beta (Si/Al = 22), 1.0 mol L À1 hydrochloric acid was added to an aqueous suspension of the zeolite, and then the pH value was adjusted to 1.0 over 3h.…”